Separation of organic acids by azeotropic distillation



1954' w. P. BURTON SEPARATION OF ORGANIC ACIDS BY AZEOTROPIC DISTILLATION Filed May 28, 1949 7 V 2 8 6 2 meta -dun M" 5 a a, I 2 a l. N. 4 M B 4 V7 W 533. 20.53553 '/w H O 3 5 mm lCO CTL AN O N INVENTOR. WILLIAM P. BURTON ATTORNEYS United States Patent sErAnn'rIoN'o ORGANIC ACIDSBY AZEOTROPIG nIsTmLArIoN William P. Burton, 0range,N. J., assignor to The M. W. Kellogg Company, Jersey City, N. J., a corporation of Delaware Application May 28, 1919, Serial No. 96,669 Claims. (Cl. 202-42) This invention relates-to the separation of organic compounds and relates more particularly to the separation of organic acids-from mixtures comprising non-acid oxygenated org'anic compounds. Still more particularly, the invention relates to the separation of organic acidshaving from 2 to 6 carbon atoms per molecule from mixtures comprising these acids and alcohols and other non-acid oxygenated organic compounds having up to 6 carbon atomsper molecule.

It is known that aqueous mixtures comprising organic acids having from 2 to 6 carbon atomsper molecule and alcohols and other non-acid oxygenated organic compoundshaving from 1' to 6 carbon atoms per molecule as the-principal acids and-non-acids, may be separated by fractional distillation, in which the mixture is charged into a fractional distillation zone, with a substantial amount of water being present to-preve'nt ester formation, to form a vapor phase and-a liquid phase, alcohols and other non-acidics being removed asvapor and acids and the bulk of'the water: present being removed-as a residue. In conducting thea' ove-meiitioned-separation in a single distillation tower, it has been found that relatively high reflux ratios ar e required to separate the relatively heavier non-acid chemicals from, the aqueous acid solution, the reflux ratio being defined as volumes of top or overhead reflux perv'olume' of distillate product. This condition is encountered by reason that the relatively less water-soluble alcohols, that is, those having from 4 to 6 or higher carbon atoms per molecule, boil close to the acids being'separated, ascornpared to the relatively low reflux ratios required for effecting separation between the acids and propanol and lower boiling alcohols. Thus, it has been found that a'reflux' ratio of at least 2: 1- is required to separate non-acid chemicals from the aqueous acid solution in etfec'tin'g fr actionaldistillation of the aforementioned aqueousmixtures. Iii-operating at a relatively high reflux ratio in the above-mentioned single stage fractional distillation, the relatively high heat requirements iinposed' on the-single piece of equipment for Ohtaining high reflux and thenecessity for employing a relatively large towenmakes such operation economically unattractive. It is hi'ghly desirable, therefore, to be able to effect separation between the aforementioned organic acids and non-acidics at a relatively lower reflux ratio and using proportionately'sm'aller distillation equipment, and in this respect is'particularly advantageous in effect ing separation between organic acids and alcohols, together with other non-acid oxygenated organic compounds, present in the Water product condensate obtained from the treatment ofthe reaction product produced in processes for the catalytic hydrogenation of oxides of carbon.

It-is, therefor-c an object of the present invention to provide for an improved method for the-economic and eflicient separation oforgariic acids having from 2 to 6 carbon atoms per molecule from mixtures comprising these acids and alcohols having up to 6 carbon atoms per molecule.

Another object of the invention is to provide for an improved method for the economic and efficient separation of organic acids having from 2 to 6 carbon atoms per molecule from fixtures comprising these acids and alcohols and other non-acid oxygenated organic compounds, having up to 6- carbon atoms per molecule.

Still another object of the invention is to provide for an improved; method for the economic and efiicient separation of organic acids andalcohols andother nonacid oxygenated organic compounds present in the water' product condensate obtained from the treatment of the reaction product produced in processes for the catalytic hydrogenation of oxides of carbon.

Qther objects and advantages inherent in the invention will be apparent to one skilled in the art from the following more detailed disclosure. p

in accordance with the broad method of the present invention, an aqueous mixture comprising one or more organic acidshaving from 2 to 6 or more carbon atoms per molecule, and one or more alcohols having from 1 to 3 carbon atoms per molecule and one or more alcohols-having from 4 to 6 or more carbon atoms per molecule, is subjected to a two-stage distillation in the presence of suiiicient water to prevent esterification between acids and alcohols and to form the corresponding water azeotropes with alcohols present, as more fully hereinafter described, in which separation is effected between acids and alcohols (together with other non-acid oxygenated organic compounds if present in the mixture to be treated) at lower reflux ratios with a resulting reduction in the total heat requirement on the system than would be required in conducting the separation in a single distillation tower. Thus in one embodiment of the invention, relatively lower boiling chemicals in the feed mixture are taken overhead in the first distillation tower. A portion of these overheads is returned as reflux to the distillation tower. Thesechemicals in the overhead comprise alcohols and other non-acidics as high boiling as propanol, while the bottoms from this distillation tower comprisesubstantially all of the acids present, and which may also contain the relatively water-insoluble alcohols and other non-acidics having from 4 to 6 carbon atoms per molecule. The bottoms thus obtained from the'first distillation tower are next fed to a second distillationtower, in the presence of sufiicient water to prevent esterification between acids and alcohols in the distillation tower, where alcohols and other non-acidics are taken overhead as their water azeotropes, while an aqueous mixture of the acids is recovered as bottoms. azeotropes may beremoved as such, with a portion thereof returned to the distillation tower as reflux, or, in another modification of the present embodiment of the method of the invention, may be subjected to phase separation in which an upper phase comprising chiefly water-insoluble alcohols and other non-acidics and a lower water rich phase comprising.water-insoluble alcohols and other non-acidics in minor proportion, is formed. This upper phase may be recovered as such, while the lower waterrichphase is returned as reflux to the second distillation step. In conducting the two-stage distillation as indicated above, it is desirable to operate the first distillation tower under such conditions of temperature andpressure-that substantially all of the propanol and other lower boiling non-acidics, if the latter are present in the original feed mixture, are taken overhead so that the bottoms from this distillation tower when subjected to the aformentioned fractionation in the second distillation tower, will be separated as overhead water azeotropes of C4 to C6 or higher non-acidics and aqueous acid bottoms. The aforementioned phase separation of the Water azcotropes thus recovered, may be omitted if so desired. However, where the distillation in the first tower is so conducted that not all of the propanol present in the feed mixture is recovered in the overheads from this tower but rather a portion thereof is also takenwith the organic acids and relatively water-insoluble C4 to C6 or higher nonacidics in, the bottoms, the aforementioned phase separation of the resulting water azeotropes from the second distillation step is employed in order to recover propanol present in theresulting water-rich phase, a portion of which is returned to the second distillation tower for reflux, as previously indicated. The mutual solubility of propanol in each layer resulting from theabovementioned phase separation of the water azeotropes recovered as overheads from the second distillation tower, has been found to result in a build-up of propanol in the system, arising from the reflux of the water-rich phase to the second distillation tower. In such event, in another modification of the embodiment of the invention, a bleedis taken from the returned layer to this These water distillation tower which carries the water-rich phase thereto as reflux. This bleed line is recycled to the first distillation step, and a build-up of propanol in the system is thus prevented.

In conducting the two-stage distillation, as described above, it has been found, as more fully hereinafter indicated, that far lower total reflux ratios are required in conducting the fractionation of acids from non-acidics than are required in conducting the fractionation in a single distillation tower. This condition is found to exist by reason that in conducting the two-stage distillation of the present invention, the relatively lighter chemicals boiling through propanol may be taken overhead in the first distillation tower at a lower reflux ratio such as 0.511, while the remaining non-acidics fractionated from the bottoms which are fed to the second distillation tower, are recovered at a relatively higher reflux ratio such as 1:1 or 2:1. This is particularly advantageous in effecting separation of alcohols and other non-acidics from organic acids present in the aforementioned water product condensate obtained from the treatment of the reaction product produced in processes for the catalytic hydrogenation of oxides of carbon. In this water product condensate the relatively lower boiling chemicals, for example, those boiling through propanol, constitute the greater proportion of the non-acid compounds present, and may comprise 90% or more of the total non-acid chemicals present in this product. Thus it is particularly desirable to be able to operate the first distillation tower at a relatively low reflux ratio such as 0.5 :1, even though the reflux ratio for the remaining chemicals in the second stage is relatively higher. The total reflux ratios thus employed, have been found to impose far lower heat requirements on the two-stage system, than if a single distillation step were employed and which has been found to necessitate a reflux ratio of at least 2:1 in order to permit complete separation of acids from non-acidics.

The accompanying drawing illustrates diagrammatically one form of the apparatus employed and capable of carrying out one embodiment of the process of the present invention. While the invention will be described in detail by reference to the embodiment illustrated in the drawing, it will be noted that it is not intended that it be limited thereto but is capable of other embodiments which may extend beyond the scope of the apparatus employed. Furthermore, the distribution and circulation of liquids and vapors is illustrated in the drawing by diagrammatic representations of the apparatus employed. Some of the mechanical elements necessary to effect the transfer of liquids and vapors and to maintain the conditions of temperature and pressure necessary to carry out the function of the apparatus, are omitted in order to simplify the description. It will be understood, however, that much equipment of this nature is necessary and will be supplied by one skilled in the art.

Referring to the drawing, a feed comprising an aqueous mixture of organic acids having from 2 to 6 carbon atoms per molecule and alcohols and other non-acid oxygenated organic compounds having from 1 to 6 carbon atoms per molecule is introduced through line 10 to a fractional distillation zone, represented by distillation tower 11. This feed may comprise a water condensate product obtained from the treatment of the reaction product produced in processes for the catalytic hydrogenation of oxides of carbon, or may comprise the aforementioned water condensate product in admixture with an extract of relatively water-soluble organic acids, alcohols and other non-acidics obtained from the treatment of the oil condensate product produced in the aforementioned catalytic hydrogenation. Thus the feed in line 10 may comprise an aqueous mixture of acetic and higher boiling acids through hexanoic acid, methanol and higher boiling alcohols through hexanol, and non-acid oxygenated organic compounds such as aldehydes (e. g., acetaldehyde, propionaldehyde, butyraldehyde), ketones (e. g., acetone, methyl ethyl ketone, methyl propyl ketone), and esters (e. g., methyl acetate, ethyl acetate, ethyl propionate), with suflicient water being present in order to avoid esterification between acids and alcohols in this tower and to form the corresponding water azeotropes with non-acidics present. Tower 11 is operated under proper conditions of temperature and pressure effective to distill overhead those non-acidics which are not higher boiling than propanol, and which in the present embodiment of the invention, may comprise methanol, ethanol and propanol as their azeotropes, as well as other non-acidics, such as aldehydes, ketones and esters (e. g., acetaldehyde, propionaldehyde, acetone, methyl ethyl ketone, ethyl acelate), boiling or azeotroping within this range. The overheads from tower 11 are transferred as vapors through line 12 to a condenser 13. Condenser 13 is provided to liquefy the vaporized mixture transferred from tower 11 through line 12. The mixture of alcohols and other nonacidics in this condenser is transferred from condenser 13, through line 14 to a reflux drum 15. From drum 15 the non-acidics thus condensed are withdrawn as an aqueous mixture through valved-line 16 for further use or treatment outside the scope of the present process. A portion of the aforementioned mixture is also transferred from line 16, via valved-line 17 with which line 16 connects, into tower 11 as reflux.

The lower relatively high boiling fraction in tower 11 will comprise acetic and higher boiling acids through hexanoic acid, butanol and higher boiling alcohols through hexanol, and other non-acidics higher boiling than propanol such as aldehydes (e. g., caproaldehyde), ketones (e. g., methyl butyl ketone), esters (e. g., ethyl butyrate). These compounds are withdrawn as aqueous bottoms from tower 11 through line 18. This aqueous mixture is next transferred through line 18 to a second fractional distillation zone, represented by distillation tower 19. In order to avoid esterification between acids and alcohols in tower 19 and to form the corresponding water azeotropes of non-acidics present, in the event that insulficient water is present in line 18, additional quantities of water may be introduced into line 18 through valved-line 20, with which line 18 connects. Tower 19 is operated under proper conditions of temperature and pressure effective to distill overhead substantially all of the C4 to Cu or higher alcohols and other non-acidics as their water azeotropes, present in line 18, and which are lower boiling than the remaining C2 to Ca or higher acids. The overhead azeotropes from tower 19 are transferred. as vapors through line 21 to a condenser 22. Condenser 22 is provided to liquefy the vaporized azeotropic mixtures transferred from tower 19 through line 21. The azeotropic mixtures thus condensed and comprising the aforementioned alcohols and non-acidics are withdrawn from condenser 22 through valved-line 23 for further use ortreatment outside the scope of the present process, or conveniently, if so desired, may be transferred from line 23 via valved-line 24 into line 16 and thus combined with the aforementioned non-acidics in this line and then withdrawn as a product of the process. A portion of the aforementioned mixture in line 23 is also transferred from line 23, via valved-line 25 with which line 23 connects, into tower 19 as reflux. Bottoms from tower 19, comprising an aqueous mixture of C2 to Cs acids, are withdrawn through line 26 as a product of the process for further use or treatment if so desired.

It should be noted that the overheads from tower 19 may be condensed and subjected to phase separation in order to essentially dehydrate the non-acidics present. The distillation in tower 11 may be so conducted that it is not practical to recover in the resulting overhead substantially all of the propanol present in the feed mixture introduced into tower 11 through line 10, but rather a portion of the propanol present is also taken with the organic acids and higher boiling non-acidics in the aqueous bottoms obtained from this tower. In such event, the previously referred to phase separation of the condensed overheads from tower 19, in another modification of the present embodiment of the invention, containing propanolwater azeotropes as additional components, are transferred directly through line 23 to a separator 27. In separator 27 as a result of settling action, there is formed an upper phase comprising C4 to C6 or higher alcohols and other relatively water-insoluble non-acidics in major proportion and water, and a lower water-rich phase comprising C4 to Ca alcohols and other relatively water-insoluble non-acidics in minor proportion. Propanol is also present in each of the aforementioned layers or phases, as a result of the mutual solubility thereof in each phase. The upper phase from separator 27 is withdrawn through line 28 and may be transferred into line 16, with which line 28 connects, and thus combined with the aforementioned nonacidics in this line and then withdrawn as a product of the process. The lower water-rich phase from separator 27 is withdrawn through valved-line 29 and returned through this line to tower 19 asreflux.

The aforementioned mutua1s61ubi1ny of -'pi'opanol in the aforementioned up'pe'rand "lower 'phas'es in separator 2-7, has been found .to resui in a buildup -of propanol in the system, thus efi'ecting its operability. In order to overcome this -factor, a bleed'is taken .from the returned-lowerlayer-to tower 1-9:a's-r'efiux. For this purposethe bleed is-takenthrough valved-line-Bt), with which line 29 connects, and 'a'portion of the'lower layer from separator '27 'is thus 'transferred through line "30 to'the feed in line 10, withwhich -line- 3ticorinects. "A -buildup of'propanol' in the system is thusprevented.

The following example indicates comparative results obtained in utilizing the two-stage distillation method of the present invention andthe results'obtainedwvith conventional single stage distillation apparatus, *Itshould' be noted however, that. the example is includedonl'yr for" the purposesof illustration and is not intended in any way 'to unduly limit the processof'the invention.

. Exampl e Employing the two-stage :distillation -.aapp.aratus illustrated in the drawing, a water condensate productbtained from the condensationof: the-reaction e'iiiuent produced by the hydrogenation oficarbon mo'noxide (in a ratio of i 1.5 parts hydrogen; and 1. part :carbon: monoxide in the presence of an alkalizeid irontcatalyst sirnilar in compositionto an ammonia synthesis catalyst) .wassintroduced into the first 'distiilationlower (tower llr in .the drawing). This water condensate product contained fatty acids boiling from acetic throughlhexanoic raci'ds, 'alcohols boiling from methanol through hexanoL'and other non-acids :comprising aldehydes, ketones and esters higher and lower boiling than propanol. tPrimary tower 11 into which this aqueousmixtur'e wasintroducecLcomprised a 1 inch diameter. column having 31 inches of packed :section below the feed pointand perforated plates above the feed point. This column was operated at a top temperature of approximately 85'C., a bottom temperature of approximately 99.5'C., and a reflux ratio of 0.67. The overhead distillate Wasfoundto be approximately 7.5 per cent of the feed, having an acidity of approximately 3.8 milliequivalents per l00ml. The bottoms from this column Were foundto contain 0.046 inilliequivalent per gram of non-acid materials, which would result in impure acids if further removal were not obtained. The second distillation tower (tower 19 in the drawing), similar in construction to tower lllemployed in the primary distillation, was operated 'at attoptemperai ture of approximately 96.5" 'C. an'da bottom "temperature of approximately 99.8" C. The total overhead, i. e., distillate andreflux, was found to be-3.2' per cent of the feed. The bottoms product from this "secondary distillation contained 0.019 non-acids, which was found to be ofsuch'concentration as would allow, simple purification to' be :made'of the recovered acids.

For comparative-purposes, the above-mentioned feed was charged to a single distillation column, having .a 1 inch diameter with 63 inches of packed section'below the feed point and 30, perforated plates above the feed point. This towerwas operated at a top temperatureof approximately'85" C., .a'bottonr temperature of approximately 100.5 C.,"and a reflux ratio of 2.33. The overhead distillate was found to contain 8 percent of the feed with an acidity of 5.6 milliequivalents per 100 ml. The bottoms product from this distillation was found to contain 0.025 milliequivalent per gram of non-acids.

From the above data the relative heat. input may be found by calculating the total chemicals distilled, i.'e., overhead product plus reflux,'for each case. With-the preliminary distillation tower operated at a '7.5 percent take-off, and 0.67 reflux ratio, itis'foun'd that .125jper centof the feed was distilled. Adding to this the 3.2 per cent quantity distilled, in thesecond tower ofitheremaining 92.5 per cent of the original feed, it is found that the total distillate for the combined operation is. 15.5 per cent of the originalfeed. For'the conventional single-tower operation, the aforementioned 8" per cent take-off at 2.33 reflux ratio, indicates that 26.6, percent of the feed was beingfdistille'doverhead. It will be noted that by feeding the' bottomsfrom-theprimary distillation tower, in the ;two-stage distillation method ofr the present invention, -to-thesecond towerwithout "cooling,

milliequivalent per gram of 6 the use or two columns would not :increase :the [quantity of sensible heat -needed for= preheating of -the feed.

While .a particular emboiiiment xo'f t11e invention .has thus been described for .purposesof illustration, it shonld be understood that various modificationscradaptations thereof, which will be obvious 1 to one skilled .in {the art, maybe made within the spirit ofthe invention asset-forth in the appended claims.

Hav'ingthus described my-invent-ion, I claim:

1. "A method for separating organic 1 acids higher boiling than *propanoltrom an aqu'eousmixture containing non-acid oxygenatedzorganic compoundsnot higher boiling and non-acid oxygenated organic compounds higher boiling than .propanol and capable of torming -waterazectropes, said mixture having been obtained as a .waterproduct condensate"produced by the catalytic hydrogenation of oxides of carbon, which comprises ina first: distillation tower, distilling said mixture in 'the presence of sufiicient W316i to prevent esterification to obtain 'a lowboiling fraction comprising non-acid 'ox-ygenatedorganic compounds not higherboilingthanpropanoland aihighboiling fraction consisting essentially of organic acids and non-acid oxygenated organic compounds "higher boiling than propanol; withdrawing each'ofsaid fractions from said distillation tower; in-a second distillation-tower, distilling saidhigh-boiling fraction inthe presence of sufficient 'water'to preventesterificationto obtain ahig'hboiling fraction comprising organic acids and alow-bOilingfraction comprisingwater-aZeotropes-of non-acid oxygenated organic compounds; withdrawingeach of said last-mentioned fractions from said second distillation'tower; and refluxing during each of said distillation steps.

2. A'method for separating organic acids higherboilin'g'than propanol from an aqueous mixture containing alcoholsan d other non-acid oxygenated organic compounds notliigheriboiling and alcohols and other nonacid oxygenated organic compoundsihigher'boilingithan propanol and capable of forming water-azeotropes, said mixturehaving been obtainedras a water-product condensate produced by; the catalytic hydrogenation of oxides of carbon, which compriseszJin a first distillationtower, distilling said mixture in the, presence of sufficient water to prevent esterification to obtain a-low boiling fraction comprising non-acid oxygenatedorganic co'mpoundsnot higher boiling'than-propanol and.a;high-'boili-ng fraction consisting essentially of organic acids and non-acidoxygenated organic compounds higher boiling than, propanol; withdrawing each of said fractionsfrom said/distillation tower;.in a second distillation tower, distilling said highboiling fraction in thepresence of sufiicientwatcr to prevent esterification to obtain a high-boilingtraction comprising organic acids and a. low-boiling-fraction comprising water-azeotropes of non-acid oxygenated organic compounds; withdrawing each -of said last-mentioned fractions from said second distillation tower; .and-refluxing during each of said distillation steps.

3. The methodforseparating organic acidshigherboiling than propanol from an aqueous nix-ture containing non-acid oxygenated organic compoundstnot higher boiling and 'non-acid'oxygenated organiccompounds higher boiling than .propanol 1 and: capable of forming water- .azeotropes, said mixture having been obtained, asa-water-product condensate produced by the catalytichydrogenation of oxides of carbon, which comprises: -,in a first distillation tower, distilling said mixture in the presenceaof sutticient'water to prevent. esterification to obtain a low-boiling fraction comprising non-acid oxygenated organic compounds nothigher boiling-than-propanol and 'a high-boiling fraction-consisting essentially of organic acids and non-acid oxygenated organic com- .pounds higher boiling than propanol; withdrawingweach of said fractionsfrom said distillation tower; inma; second distillation tower, distilling saidhigh-boiiing traction in the presence of sufiicient watertoprevent esteriiication to obtain'a-high-boiling fraction comprising organic acids and a low-boiling fraction comprising water-azeotropes of' noncid oxygenated organic compounds; withdrawing each or said last-mentioned fractions fromsaid sccond distillation tower; separating said azeotropes intoanupper phase and'a lower water-rich phase, eachof said phases comprising non-acid oxygenated organic compounds; returning, a portion of said water-rich phase to at least one of'said distillation towers; andrefittring dur ing each of said distillation steps.

4. A method for separating organic acids higher boiling than propanol from an aqueous mixture containing non-acid oxygenated organic compounds not higher boiling and non-acid oxygenated organic compounds higher boiling than propanol and capable of forming waterazeotropes, said mixture having been obtained as a waterproduct condensate produced by the catalytic hydrogenation of oxides of carbon, which comprises: in a first distillation tower, distilling said mixture in the presence of sufficient water to prevent esterification to obtain a low-boiling fraction comprising non-acid oxygenated organic compounds not higher boiling than propanol and a high-boiling fraction consisting essentially of organic acids and non-acid oxygenated organic compounds higher boiling than propanol; withdrawing each of said fractions from said distillation tower; in a second distillation tower, distilling said high-boiling fraction in the presence of suflicient water to prevent esterification to obtain a high-boiling fraction comprising organic acids and a low-boiling fraction comprising water-azeotropes of nonacid oxygenated organic compounds; withdrawing each of said last-mentioned fractions from said second distillation tower; separating said azeotropes into an upper phase and a lower water-rich phase, each of said phases comprising non-acid oxygenated organic compounds; returning a portion of said water-rich phase to said first distillation tower; and refluxing during each of said distillation steps.

5. A method for separating organic acids higher boiling than propanol from an aqueous mixture containing non-acid oxygenated organic compounds not higher boiling and non-acid oxygenated organic compounds higher boiling than propanol and capable of forming waterazeotropes, said mixture having been obtained as a waterproduct condensate produced by the catalytic hydrogenation of oxides of carbon, which comprises: in a first distillation tower, distilling said mixture in the presence of sufiicient water to prevent esterification to obtain a low-boiling fraction comprising non-acid oxygenated organic compounds not higher boiling than propanol and a high-boiling fraction consisting essentially of organic acids and non-acid oxygenated organic compounds higher boiling than propanol; withdrawing each of said fractions from said distillation tower; in a second distillation tower, distilling said high-boiling fraction in the presence of sufficient water to prevent esterification to obtain a high-boiling fraction comprising organic acids and a low-boiling fraction comprising water-azeotropes of nonacid oxygenated organic compounds; withdrawing each of said last-mentioned fractions from said second distillation tower; separating said azeotropes into an upper phase and'a lower water-rich phase, each of said phases comprising non-acid oxygenated organic compounds; returning a portion of said water-rich phase to said second distillation tower; and refluxing during each of said distillation steps.

6. A method for separating organic acids higher boiling than propanol from an aqueous mixture containing alcohols and other non-acid oxygenated organic compounds not higher boiling and alcohols and other nonacid oxygenated organic compounds higher boiling than propanol and capable of forming water-azeotropes, said mixture having been obtained as a water-product condensate produced by the catalytic hydrogenation of oxides of carbon, which comprises: in a first distillation tower, distilling said mixture in the presence of sufficient water to prevent esterification to obtain a low-boiling fraction comprising non-acid oxygenated organic comounds not higher boiling than propanol and a highboiling fraction consisting essentially of organic acids and non-acid oxygenated organic compounds higher boiling than propanol; withdrawing each of said fractions from said distillation tower; in a second distillation tower, distilling said high-boiling fraction in the presence of suflicient water to prevent esterification to obtain a high-boiling fraction comprising organic acids and a lowboiling fraction comprising water-azeotropes of nonacid oxygenated organic compounds; withdrawing each of said last-mentioned fractions from said second distillation tower; separating said azeotropes into an upper phase and a lower water-rich phase, each of said phases comprising non-acid oxygenated organic compounds; returning a portion of said water-rich phase to at least one of said distillation towers; and refluxing during each of said distillation steps.

7. A method for separating organic acids having from 2 to 6 carbon atoms per molecule from an aqueous mixture containing propanol and higher and lower boiling and non-acid oxygenated organic compounds having from 1 to 6 carbon atoms per molecule, which comprises: in a first distillation tower, distilling said mixture in the presence of suflicient water to prevent esterification to obtain a low-boiling fraction comprising propanol and lower boiling non-acid oxygenated organic compounds and a high-boiling fraction consisting essentially of organic acids, propanol, and higher boiling non-acid oxygenated organic compounds; withdrawing each of said fractions from said distillation tower; in a second distillation tower, distilling said high-boiling fraction in the presence of sufiicient water to prevent esterification to obtain a high-boiling fraction comprising organic acids and a low-boiling fraction comprising water-azeotropes of non-acid oxygenated organic compounds; withdrawing each of said last-mentioned fractions from said second distillation tower; separating said azeotropes into an upper phase comprising non-acid oxygenated organic compounds having from 4 to 6 carbon atoms per molecule and a lower water-rich phase comprising propanol; returning a portion of said water-rich phase to at least one of said distillation towers; and refluxing during each of said distillation steps.

8. A method for separating organic acids having from 2 to 6 carbon atoms per molecule from an aqueous mixture containing propanol and higher and lower boiling and non-acid oxygenated organic compounds having from 1 to 6 carbon atoms per molecule, which comprises: in a first distillation tower, distilling said mixture in the presence of suflicient water to prevent esterification to obtain a low-boiling fraction comprising propanol and lower boiling non-acid oxygenated organic compounds and a high-boiling fraction consisting essentially of organic acids, propanol, and higher boiling non-acid oxygenated organic compounds; withdrawing each of said fractions from said distillation tower; in a second distillation tower, distilling said high-boiling fraction in the presence of sufiicient water to prevent esterification to obtain a high-boiling fraction comprising organic acids and a low-boiling fraction comprising water-azeotropes of non-acid oxygenated organic compounds; withdrawing each of said last-mentioned fractions from said second distillation tower; separating said azeotropes into an upper phase comprising non-acid oxygenated organic compounds having from 4 to 6 carbon atoms per molecule and a lower water-rich phase comprising propanol; returning a portion of said water-rich phase to said first distillation tower; and refluxing during each of said distillation steps.

9. A method for separating organic acids having from 2 to 6 carbon atoms per molecule from an aqueous mixture containing propanol and higher and lower boiling and non-acid oxygenated organic compounds having from 1 to 6 carbon atoms per molecule, which comprises: in a first distillation tower, distilling said mixture in the presence of suflicient water to prevent esterification to obtain a low-boiling fraction comprising propanol and lower boiling non-acid oxygenated organic compounds and a high-boiling fraction consisting essentially of organic acids, propanol, and higher boiling non-acid oxygenated organic compounds; withdrawing each of said fractions from said distillation tower; in a second distillation tower, distilling said high-boiling fraction in the presence of sufficient water to prevent esterification to obtain a high-boiling fraction comprising organic acids and a lowboiling fraction comprising water-azeotropes of non-acid oxygenated organic compounds; withdrawing each of said last-mentioned fractions from said second distillation tower; separating said azeotropes into an upper phase comprising non-acid oxygenated organic compounds having from 4 to 6 carbon atoms per molecule and a lower water-rich phase comprising propanol; returning a portion of said water-rich phase to said second distillation tower; and refluxing during each of said distillation steps.

10. A method for separating organic acids having from 2 to 6 carbon atoms per molecule from an aqueous mixture containing higher and lower boiling non-acid oxygenated organic compounds having from 1 to 6 carbon atoms per molecule, said higher boiling non-acid compounds being capable of forming water-azeotropes, which comprises: in a first distillation tower, distilling said mixture in the presence of sufficient water to prevent esterification to obtain a low-boiling fraction comprising non-acid oxygenated organic compounds having from 1 to 3 carbon atoms per molecule and a high-boiling fraction consisting essentially of organic acids and non-acid oxygenated organic compounds having from 3 to 6 carbon atoms per molecule; withdrawing each of said fractions from said distillation tower; in a second distillation tower, distilling said high-boiling fraction in the presence of sufiicient water to prevent esterification to obtain a high-boiling fraction comprising organic acids and a low-boiling fraction comprising water-azeotropes of nonacid oxygenated organic compounds; withdrawing each of said last-mentioned fractions from said second distillation tower; separating said azeotropes into an upper phase comprising non-acid oxygenated organic compounds having from 4 to 6 carbon atoms per molecule and a lower water-rich phase comprising non-acid oxygenated organic compounds having 3 carbon atoms per molecule; returning a portion of said water-rich phase to at least one of said distillation towers; and refluxing during each of said distillation steps.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,204,652 Bludworth June 18, 1940 2,324,755 Beamer July 20, 1943 2,438,300 Schniepp Mar. 23, 1948 2,457,257 Michael Dec. 28, 1948 2,476,788 White July 19, 1949 2,523,248 Heinze et al Sept. 19, 1950 2,533,675 Marschner Dec. 17, 1950 OTHER REFERENCES Robinson, Elements of Fractional Distillation, sec- 0nd edition, published 1930 by McGraw-I-Iill Book Company, New York, New York, pages 133-138. 

1. A METHOD FOR SEPARATING ORGANIC ACIDS HIGHER BOILING THAN PROPANOL FROM AN AQUEOUS MIXTURE CONTAINING NON-ACID OXYGENATED ORGANIC COMPOUNDS NOT HIGHER BOILING AND NON-ACID OXYGENATED ORGANIC COMPOUNDS HIGHER BOILING THAN PROPANOL AND CAPABLE OF FORMING WATERAZEOTROPES, SAID MIXTURE HAVING BEEN OBTAINED AS A WATERPRODUCT CONDENSATE PRODUCED BY THE CATALYTIC HYDROGENATION OF OXIDES OF CARBON, WHICH COMPRISES: IN A FIRST DISTILLATION TOWER, DISTILLING SAID MIXTURE IN THE PRESENCE OF SUFFICIENT WATER TO PREVENT ESTERIFICATION TO OBTAIN A LOWBOILING FRACTION COMPRISING NON-ACID OXYGENATED ORGANIC COMPOUNDS NOT HIGHER BOILING THAN PROPANOL AND A HIGHBOILING FRACTION CONSISTING ESSENTIALLY OF ORGANIC ACIDS AND NON-ACID OXYGENATED ORGANIC COMPOUNDS HIGHER BOILING THAN PROPANOL; WITHDRAWING EACH OF SAID FRACTIONS FROM SAID DISTILLATION TOWER; IN A SECOND DISTILLATION TOWER, DISTILLING SAID HIGH-BOILING FRACTION IN THE PRESENCE OF SUFFICIENT WATER TO PREVENT ESTERIFICATION TO OBTAIN A HIGHBOILING FRACTION COMPRISING ORGANIC ACIDS AND A LOW-BOILING FRACTION COMPRISING WATER-AZEOTROPES OF NON-ACID OXYGENATED ORGANIC COMPOUNDS; WITHDRAWING EACH OF SAID 